Process of generating a depressed bifocal lens



'Feb. 17. 1925.

1,526,898 L. W. BUGBEE PROCESS OF GENERATING A DEPRESSED BIFOCAL LENS Filed July 5, 3

H *FIEi. E

' INVENTOR. Auc/fi/v W 50685:.

A TTORNEYJ.

Patented Feb. 17, 1925.

UNITED STATES- PATENT OFFICE.

LUCIAN W. BUGBEE, OF INDIANAPOLIS, INDIANA, ASSIGNOR T ONEPIEGE BIFOGAL LENSOOMPAN'Y, OF INDIANAPOLIS, INDIANA, A CORPORATION.

PROCESS OF GENERATING A DEPNESSED IBIFOCAL LENS.

Application filed July 5, 1823. 'serial No. 649,650.

State of Indiana, have invented a certain new and useful Process of Generating a Depressed Bifocal Lens; and I do hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying drawings, in,

which like numerals refer to like parts.

The object of this invention is to cheapen the manufacture of what are known as deressed onepiece bifocallenses, that is, such enses with the reading field depressed relative to the distance field. This process shortens the time required to form and 01- ish the reading field and form the shou der between the two fields. i The chief feature of the invention consists in grinding the reading field smaller in diameter than desired,with a slightly raised surface at the middle of the reading field. Then the reading field'is ground and the shoulder formed by a grinding button of a diameter slightly greater than the radius of thereading field so that when it is placed on the slightly raised surface on the center of the reading field, it will reach beyond the margin of the reading field and overlap a portion of the surround.- ing or distance field and grind it away to form a shoulder.

In the process heretofore employed in this art to make such lenses, the blank was ground so that the reading surface at the beginning would have its full required diameter, as shown by Letters Patent to me, No. 1,487,715, dated March 25, 1924, and thereafter a grinding button substantially one-half the diameter of the reading field was required to be employed to grind the whole reading surface away until the required depression of the reading field and size of the shoulder were produced. The object of the present invention is to quicken and cheapen the manufacture of such lenses by shortening the last operation referred to, namely, that of generating the reading segment so as to epress itv and provide the desired shoulder.

The full nature of the invention will be understood from. the accompanying drawilligs and the following description and C was:

' In'the drawings, Figure 1 is a central section of a target blank for making depressed bifocal lenses, showin the same in the finished form of a blan Fig. 2 is the blank at the end of the first grinding operation; Fig. 3 is a side view of the grinder for primarily generating the two bifocal surfaces. Fig. 4 is a section of a central portion of Fig. 2 on an enlarged scale with the button grinder in place thereon. Fig. 5 is similar to Fig. 4 after the button grinder has operated.

The blank sought to be formed is shown in Fig. 1 and consists of a single piece of glass of target form which has been finished on the bifocal side thereof so as to have a central depressed reading field and a surrounding distance field 11 The target blank shown in Fig. 1 is not finished on the opposite side, but said target blank is centrally split and the two halves thereof sold and shipped from the manufacturer to the It is observed that in this type of onepiece bifocal lens blank, see Fig. 5, the reading field is depressed with reference to the distance field so that there is a distinct shoulder 12 at the division between the two fields. Heretofore in making these lenses one method which has been employed has been simultaneously grind and generate roughly the two bifocal surfaces so that they practically merge into each other. In that form, the center of the readingfield is lower than any other part of the reading field or of the lens blank. Then in the second step of the operation the reading field was further ground so as to depress the-reading field and make the shoulder 12, as shown in Fig. 5. The reading field in this form as originally ground was of the full required diameter of the reading field in the finished blank and the grinding button was required to grind the whole reading surface awa until the required depth of the reading fiel and elevation of the shoulderwas attained. One drawback in this old operation was that the grinding button ground faster at the center of the reading field than it did at the margin thereof and that trouble, in addition to the long grinding operation necessary to grind the reading surface entirel away, increased the-expensiveness of sai lenses.

In the present invention I make the grinder 15 with a shallow recess 16 concentric of the zone 17 which generates the central part of the tar et blank. This leaves a slightly raised sur ace 18 at the middle of the reading field shown in Figs. 2 and 4. Also the zone 17 of the grinder is made relatively narrower than the diameter of the desired reading segment so that it produces a relatively narrow reading segment or portion. A grinding button 14 of the usual size for said reading segment is next employed for further grinding and generating the reading segment. This button is one-half the diameter of the ultimate and desired reading field, but is of greater diameter than one-half of the diameter of the reading field shown in Figs. 2 and 4, as generated in. the first operation in this process. 4

Hence the button 14 in this process overlaps the edge of the distance field somewhat, as shown in Fig. 4. It extends from the raised surface 18 at the center of the reading field to a point two or three m. m. beyond the margin of the reading field which results from the-first grinding operation. The intermediate portion of the button 14 does not touch the reading field for in generating the reading field in the first operation,

I as seen in Fig. 2, it has been ground down function of the second operation, employor depressed to some extent. The chief ing the grinding button 14, is to grind the shoulder so as to make the reading field of the desired diameter and make the shoulder sharp and accurate. Therefore, all the grinding that is necessary in this second operation, according to the present invention, is the grinding down of the distance field at the shoulder and of the slightly raised surface 18 at the center of the reading field. This grinding is a very short operation because the body of the grinding button does not have to grind away any of the glass. The central raised surface 18 alsoserves to prevent the grinding button from di ging into the center of the reading field an thus changing the curvature thereof. Preferably the size of this raised surface 18 should be such that it would take the grinding button to remove it and form the shoulder 12. By this process the required shoulder is obtained in about one-tenth of the time required by the old process, and there is also less danger of changing the curvature of the reading field.

The invention claimed is:

1. In the process of making bifocal lenses, generating the distance field and reading field with the diameter of the reading field less than the desired ultimate diameter thereof and with a raised surface at the center of the reading field, and simultaneously grinding away said raised surface and a concentric portion of the distance field to form the shoulder.

2. In the process of making bifocal lenses, generating the distance field and reading field with the diameter of the reading field less than the desired ultimate diameter thereof and with a raised surface at the center of the reading field, and further grinding the reading field by a grinding tool having half the ultimate diameter of the reading field and placing one edge of said grinding tool on said raised surface at the center of the reading field and the opposite edge of said button overlapping the adjacent edge of the distance field.

3. In the process of making bifocal lenses, generating the distance field and reading field with the diameter of the reading field less than the desired ultimate diameter thereof and with a raised surface at the center of the reading field, and further grinding the reading field by a grinding tool having half the ultimate diameter of the reading field and placing one edge of said grinding tool on said raised surface at the center of the reading field and the opposite edge of said button overlapping the adjacent edge of the distance field and not touching the reading field between said opposite edges of the button until the grinding operation is substantially completed.

In witness whereof, I have hereunto affixed my signature.

LUCIAN W. BUGBEE. 

